Procedure for the operation of combustion engine

ABSTRACT

An improved process and apparatus for preparing a gaseous mixture of hydrocarbon and carbon monoxide to be supplied to the air/fuel mixture of a combustion engine is disclosed. The process and apparatus are useful in reducing the amount of noxious components and aldehydes in the engine exhaust gas. In one embodiment of the invention, an improved process and combustion engine are provided for reducing the noxious components and aldehydes. Recycled, water vapor-containing exhaust gas is mixed with at least one lower alcohol. Subsequently, the lower alcohol is catalytically steam reformed in the presence of the exhaust gas to form a gaseous mixture of hydrogen and carbon monoxide, at least a portion of the water vapor and energy required for the steam reforming being provided by the exhaust gas. The hydrogen/carbon monoxide mixture is combined with a mixture of air and a disparate primary engine fuel, and the combined mixture is supplied to a combustion zone wherein the mixture is combusted to produce an exhaust gas having a reduced amount of noxious components and aldehydes. Preferably, the lower alcohol is methanol, the primary fuel is gasoline, and the steam reforming is carried out in the presence of a noble metal catalyst or a nickel catalyst.

In the past years methanol has received attention as an additive togasoline. Methanol has a high octane number and it is therefore possibleto replace the lead additive in gasoline with an additive having up to20% methanol. In this way, the lead emissions in the exhaust gas areeliminated. Also, there will be a lower content of nitrogen oxides,carbon monoxides and unburnt hydrocarbons in the exhaust gas.

Another approach to improving the exhaust gas quality is to add hydrogento the combustion engine. Hydrogen addition makes it possible to operateat a higher air to fuel ratio resulting in a lower content of unburnthydrocarbons and carbon monoxide. A particularly advantageous procedureto supply hydrogen is described in my earlier U.S. Pat. No. 3,918,412.According to that patent, hydrogen is produced by steam reforming of apart of the fuel in a catalytic reactor by reaction with steam andcarbon dioxide. A portion of the exhaust gas is recirculated to thecatalytic reactor where it is mixed with part of the liquid fuel whichthen is converted to hydrogen and carbon monoxide. This procedure givesimproved fuel economy and good control of unburnt hydrocarbons andcarbon monoxide as well as of nitrogen oxides. It is also disclosed inmy earlier patent that lower alcohols can be used as fuel. Part of thealcohol fuel is supplied directly to the combustion engine and part ofit to the catalytic reactor for steam reforming to hydrogen and carbonmonoxide.

A serious drawback with the alcohol fuels is their low energy content.One liter of gasoline is equivalent to two liters of methanol whichmeans that a methanol fuel car must carry twice as much fuel tanks as acorresponding gasoline car.

The method as discussed above comprising supplying a small quantity ofmethanol to gasoline may therefore be considered as a good compromisewhich meets the requirement for high energy content of the fuel as wellas the requirements for good environmental qualities. The advantages anddrawbacks of methanol addition to gasoline for cars are presently beingevaluated. The present state of the art is reported in the proceedingsfrom the seminar "Methanol as a Fuel," conducted in Stockholm Mar. 21,22 and 24, 1976. In these proceedings, the environmental advantages ofsuch processes were elucidated. Also, a number of practical problemswhich must be solved in changing to a methanol additive in gasoline werediscussed.

Several different problems exist. One well known problem is the risk ofphase separation. This depends partly on the composition of the gasolineand partly on its water content. It is difficult to prevent water vaporfrom coming into the tank and other spaces carrying fuel. The methanoladditive also produces special materials problems. For instance, theadditive produces corrosion on light metal components and otherwiseaffects components made of polymers and rubbers in systems such as thefuel system. By choice of proper materials which are resistant in theparticular chemical environment, these material problems may be solved.The advantages with the methanol additives are of course dependent onthe chemical composition and reactivity of methanol. The most difficultmotor problems also depend on the inherent properties of the methanol.The high vapor pressure of methanol thus gives differences in themethanol-gasoline distribution between the different cylinders in theengine. The high heat of evaporation of methanol produces cooling of thecomponents where methanol is being vaporized. These problems requireconsiderable redesign of the combustion engine, which in turn prevents afast introduction of the new motor fuel. Increased motor wear has alsobeen observed and it appears that some lead should be added to thegasoline to overcome this problem.

The methanol additive is not completely free of problems from anenvironmental point of view in spite of reduced emissions of unburnthydrocarbons, carbon monoxide and nitrogen oxides. Small quantities ofaldehydes are produced in the combustion and the influence of thesealdehydes on the environment and public health has not been clarified.

Pure hydrogen would of course be an ideal motor fuel from manyviewpoints, and is the subject of considerable interest. The primedifficulty is, however, the storage. The hydrogen would occupy a volumewhich is at least as large as the volume of, for example, methanol withthe same energy content. To convert a more energy-rich fuel likegasoline to 100% hydrogen requires a process system of a considerablesize. The ideal would of course be if motor fuel could be supplied witha hydrogen additive instead of the methanol additive being discussedabove. This would provide a compromise meeting all the conflictingrequirements which are put on motor fuel as discussed above. It is not,however, possible to bind hydrogen in gasoline.

The drawback associated with my earlier U.S. patent referred to abovewhen used with gasoline is the comparatively high temperature needed forsteam reforming. This, among other things, has the effect of producing alow energy recovery from the exhaust gas steam. Application of theinvention disclosed in my earlier patent to alcohol fuels, on the otherhand, requires comparatively large volumes for, e.g., the fuel tanks.

While this invention is related to the method of supplying methanol togasoline and the method of supplying hydrogen to the fuel-air mixtureaccording to my earlier U.S. Pat. No. 3,918,412, it eliminates theproblems which are connected with methanol addition to gasoline asdescribed above as well as other problems which are associated with theprocedure according to U.S. Pat. No. 3,918,412.

In the description which follows, it is noted that the present inventionuses the same primary fuels as are normally used in methanol addition togasoline.

One object of the present invention is to eliminate the risk for phaseseparation in methanol-gasoline mixtures.

A second object is to reduce corrosion and material changes in the fuelsystem of the engine.

A third object is to eliminate the uneven distribution of fuelcomponents between the different cylinders of the engine.

A fourth object is to eliminate the risk for vapor lock and freezing of,e.g., the carburetor, caused by the high heat of vaporization of themethanol.

A fifth object is to improve the fuel economy by utilization of part ofthe energy content of the exhaust gases.

A sixth object is to improve the quality of the exhaust gas associatedwith the methanol addition to gasoline by eliminating or at leastdrastically reducing the aldehyde emissions.

A seventh object is to allow freedom in the choice of the composition ofthe motor fuels.

An eight object of the invention is to make possible a simple rebuildingof existing engines.

A ninth object is to require only simple modification of thedistribution system and fuel supply system to convert to the new fuelsystem.

In one aspect of this invention a process is provided for reducing theamount of noxious components and aldehydes in the exhaust gas of anoperating combustion engine. A water vapor-containing exhaust gas streamfrom the combustion engine is recycled to a first zone wherein theexhaust gas stream is mixed with a separate feed stream comprising atleast one lower alcohol. The lower alcohol containing feed stream iscatalytically steam reformed in a steam reforming zone in the presenceof said exhaust gas stream to form a gaseous mixture comprising hydrogenand carbon monoxide, whereby at least a portion of the water vapor andenergy required for said steam reforming is provided by said exhaust gasstream. The gaseous mixture of hydrogen and carbon monoxide is combinedwith a mixture of air and a disparate primary engine fuel, and thehydrogen/carbon monoxide/air/primary fuel mixture is supplied to acombustion zone within said combustion engine. The mixture is combustedin said combustion zone to produce an exhaust gas comprising a reducedamount of noxious components and aldehydes.

In another aspect of the present invention, an improved combustionengine is provided which emits an exhaust gas containing a reducedamount of noxious components and aldehydes. The combustion enginecomprises means operatively connected to a first zone for recycling awater vapor-containing exhaust gas stream thereto. Means are providedfor introducing into said first zone a separate feed stream to be mixedwith said exhaust gas stream, which separate feed stream comprises atleast one lower alcohol. Means are also provided within said first zonefor catalytically steam reforming said lower alcohol-containing feedstream in the presence of said exhaust gas stream to form a gaseousmixture comprising hydrogen and carbon monoxide, whereby at least aportion of the water vapor and energy required for said stream reformingis provided by said exhaust gas stream. Adjacent to said first zone,means are disposed for combining said gaseous mixture of hydrogen andcarbon monoxide with a mixture of air and disparate primary engine fuel.Operatively connected to said combining means are means for supplyingthe hydrogen/carbon monoxide/air/primary fuel mixture to a combustionzone within said combustion engine. Finally, means for combusting saidmixture in said combustion zone to produce an exhaust gas comprising areduced amount of noxious components in the aldehydes are provided.

In yet another aspect of the present invention, an improved combustionengine with exhaust gas recirculation is provided. The improvement is asfollows: means are provided for mixing a feed stream comprising at leastone lower alcohol with a water vapor-containing exhaust gas stream in afirst zone. Within said first zone, means are provided for catalyticallysteam reforming said lower alcohol-containing feed stream in thepresence of said exhaust gas stream to form a gaseous mixture comprisinghydrogen and carbon monoxide, whereby at least a portion of the watervapor and energy required for said steam reforming is provided by saidexhaust gas stream. Disposed adjacent to said first zone are means forcombining said gaseous mixture of hydrogen and carbon monoxide with amixture of air and a disparate primary engine fuel. Operativelyconnected to said combining means are means for supplying thehydrogen/carbon monoxide/air/primary fuel mixture to a combustion zonewithin said combustion engine. Finally, means are provided forcombusting said mixture in said combustion zone to produce an exhaustgas comprising a reduced amount of noxious components and aldehydes.

All these highly desired advantages and properties are produced by meansof the present invention in an extremely simple and surprising way. Theessence of the present invention is a combination of several factors.One important factor is that the methanol is never mixed with thegasoline but is distributed separately and contained in a special tankon the vehicle. The second factor is that most of the methanol ischanged to hydrogen and carbon monoxide in a special catalytic reactorwhereafter the gaseous mixture is supplied to the engine, e.g., bymixing the gasoline-air-fuel mixture in the carburetor. The third factoris that the methanol is converted to hydrogen and carbon monoxide byreaction with water vapor in the recirculated exhaust gas. If the rateof recirculation is to be reduced, it is possible to supply additionalwater to the methanol. A fourth important factor is that the steamreforming of the methanol may proceed at a comparatively low temperatureof about 300° C. This makes possible recovery of an important part ofthe energy content of the exhaust gas by direct and possibly alsoindirect contact between the reaction mixture and the exhaust gasstream.

The invention thus consists of a new method to produce a gas mixturecontaining hydrogen and carbon monoxide to be added to the fuel/airmixture for a combustion engine for the purpose of reducing the contentof noxious components in the exhaust gases given off from the combustionengine. The invention is characterized by the hydrogen and the carbonmonoxide being produced by steam reforming of methanol in a catalyticreactor, by at least part of the requirement of water vapor for thesteam reforming and also the energy for the reaction being satisfied bysupplying exhaust gas from the combustion engine to the catalyticreactor where it is mixed with the methanol and by the methanol beingsupplied from a special methanol system containing a tank, conduits andfeeding means for the supplying of methanol to the catalytic reactor.

The invention shall now be described in more detail by means of theaccompanying single FIGURE which shows means for carrying out theprocedure according to the invention.

The engine 1 is supplied by an inlet pipe 2 having a choke 3. Thegasoline is supplied from a gasoline tank 4 by means of a conduit 5containing a fuel pump 6 to a carburetor 7 in a known manner. Theexhaust gases leave the engine via the exhaust gas stream forrecirculation. The flow is controlled by means of, e.g., a choke 11 tothe catalytic reactor 12 which contains a catalyst 13. Methanol is alsosupplied to the catalytic reactor from a methanol tank 14 by a conduit15 which contains a feeding means 16. A conduit 17 carries recirculatedexhaust gas as well as hydrogen, carbon monoxide a non-reacted methanolto the inlet pipe 2.

It may be of advantage to vaporize the methanol prior to feeding it intothe catalytic reactor 12. The FIGURE shows a vaporizer 18 in the conduit15 which may be employed for this purpose. Heat is supplied to thevaporizer from the exhaust gas flow.

It was mentioned above that it is sometimes of advantage to supplyadditional water to the catalytic reactor. The FIGURE also shows a watertank 19 which may be used to supply the catalytic reactor 12 withadditional water via a conduit 20 with a feeding means 21.

There exist several possibilities to carry out the startup procedure.One possibility is to start up the system on methanol and then convertto two-fuel operation when the catalyst has obtained a temperature ofabout 300° C. To start on methanol, the FIGURE also shows a separateconduit 22 which may be employed when the system is started up onmethanol. The conduit contains a valve 23 controlled by a temperatureindicator 24. A similar valve in the gasoline system, which valve is notshown in the FIGURE, prevents supply of gasoline to the engine until thecatalytic reactor has attained its temperature of operation, whereafterthe direct methanol supply is shut off by means of the valve 23.

Combustion engines with exhaust gas recirculation are available on themarket and represent technology known to those skilled in this art.Therefore, no more details are required. A description of thistechnology is given, e.g., in U.S. Pat. No. 3,294,073.

The methanol system, including the catalytic reactor, is thus animprovement to a known combustion engine with exhaust gas recirculation.Since part of the combustion energy is derived from the methanol, it isnecessary to reduce the supply of gasoline to the carburetorcorrespondingly by adjusting the carburetor. It is frequently useful towork with a volume flow of methanol which is about 5-30% of the volumeflow for the gasoline. A particularly advantageous range is 10-20% ofthe volume flow for the gasoline which is equivalent to 5-10% of thecombustion energy derived from the methanol.

Methanol is of course a particularly good fuel for use in the presentinvention based on its low production costs and the ability to producemethanol from a large number of solid fuels ranging from coal tomunicipal refuse. The invention is, however, not limited to methanol butmay equally well be applied to other lower alcohols, e.g., ethylalcohol, isopropanol or similar lower alcohols and mixtures thereof. Socalled methyl fuel may also be used. Methyl fuel is composed mainly ofmethyl alcohol but also contains a minor part of higher alcohols. Thedescription which follows will use as an exemplary fuel methanol, i.e.,technical fuel in which a major part, i.e., about more than 90%, iscomposed of methyl alcohol. The methanol may additionally contain water,in some cases up to about 50%, so as to support the steam reformingreaction and reduce the exhaust gas recirculation.

Since the methanol never comes into contact with the main fuel of theengine in its liquid state, there are no restrictions on the choice ofthe main fuel for the combustion engine. It is therefore possible to usedifferent kinds of fuels, e.g., gasoline, diesel oil and other energyrich liquid fuels.

Furthermore, there are no restrictions as regards the design of thecombustion engine and its principal function. The invention may thus beapplied equally as well with Otto-engines as with diesel engines,Wankel-engines, gas turbines and other combustion engines with internalcombustion of the fuel.

The catalytic reactor is a central component in the present system whichis used in the application of the invention. This reactor is adequatelydescribed in the U.S. Pat. No. 3,918,412. In the present invention,however, only the methanol is added to the catalytic reactor, from asingle tank. The main fuel is added directly to the engine from anothertank via its own feeding means.

Methanol is particularly advantageous in minimizing problems with sootformation and also starting up as compared to the case when gasoline isused for the steam reforming reaction.

It should be noted here that it may be desirable to additionallyincorporate a certain amount of lead in the gasoline to eliminate wearproblems which sometimes arise with completely lead-free gasoline. Whensuch lead-containing gasoline is used with the procedure according tothe U.S. Pat. No. 3,918,412, the catalyst may be poisoned after a longperiod of operation. (However, there are some catalysts developed forexhaust gas cleaning with leaded gasoline. These catalysts may alsoproduce certain steam reforming effect when used as catalysts for theprocedure according to the present invention.) Suitable catalysts aredisclosed, e.g., in U.S. Pat. No. 3,918,412. The catalyst which isdescribed in the U.S. Pat. No. 3,828,736 has also proven to be usefulwith the procedure according to the present invention. Particularlyuseful catalysts are noble metal catalysts on carriers and noble metalcatalysts on pellets, but nickle catalysts may also be used atadvantage.

A special advantage with nobel metal based catalysts is their betteroxidation resistance in the presence of residual oxygen in the gasmixture which is supplied to the catalytic reactor compared to, forinstance, nickel based catalysts. The temperature of operation dependson the type of catalyst and the kind of alcohol fuel. It is normallywithin the range of 200°-600° C., preferably within the range of250°-400° C. and most preferably within the range of 275°-350° C. withmethanol and a noble metal catalyst.

EXAMPLE 1

This invention has been demonstrated in a motor rig at the RoyalInstitute of Technology in Stockholm. The engine, a four cylinder VolvoB20 A, was placed in a test rig. The power from the motor was dissipatedby means of a brake generator delivering the electrical energy to a loadresistance. The outgoing exhaust gas was analyzed by means of gaschromatographs and an IR- analytical instrument (URAS-2) for nitrogenoxides. This engine is normally equipped with exhaust gas recirculation.An Engelhard PTX exhaust gas reactor was mounted in the pipe for exhaustgas recirculation and the reactor was insulated. The exhaust gas flowwas calibrated by means of a valve. The nozzles in the carburetor hadbeen replaced to give a reduction of the gasoline flow to 95% of thenormal flow for this engine when using 100% gasoline. The methanol wasfed from a special tank and vaporized in the vaporizer 18, principallyshown in the FIGURE, before the introduction into the catalytic reactor12. The engine was run at an air/fuel ratio of 1.2 whereby the methanolflow was adjusted to amount to 10% of the flow of gasoline on a volumebasis.

At 5.8 kW output power, exhaust gas contained 0.2% CO, about 0.02%nitrogen oxide and only traces of unburnt hydrocarbons.

It was not possible to run the engine at this high air/fuel ratio onstraight gasoline in the conventional manner without misfire.

EXAMPLE 2

A similar experiment was run at 7.2 kW output power with an air-fuelratio as high as 1.55. In this experiment the noble metal catalyst wassubstituted for a commercial nickel catalyst, Girdler G 56, whichattained a temperature of operation of 690° C. The methanol feed was 35%of the gasoline feed on a volume basis. The exhaust gas contained 0.16%CO, 25 ppm unburnt hydrocarbons and non-detectable NO_(x), that is below10 ppm. The fuel consumption was about 15% less than for a correspondingconventional run with operation on straight gasoline and exhaust gascleaning. The flow of recirculated exhaust gas was 5.4% of the totalexhaust gas stream. Experimental runs with the nickel catalyst reactorwere carried out with methanol feeds up to 60% of the volumetric flow ofgasoline with the same outstanding results.

These very spectacular results were also obtained when the methanol wassubstituted for ethanol and isopropanol.

As compared to the procedure according to the U.S. Pat. No. 3,918,412,the present invention provides a simplified start up procedure and alsoa reduction of harmful emissions during the starting period. Thecatalyst reached the temperature of operation within 10-20 seconds.

In the Examples described above no special precautions were taken forthe starting procedure. One precaution would be, however, to delaysupplying the methanol feed to the catalytic reactor until the reactorhas reached the temperature of operation. This could be done by means ofa temperature indicator controlling a shut-off valve in the methanolpipe. Another precaution would be to start the engine on methanol andthen go over to dual-fuel operation when the catalytic reactor hasreached the temperature of operation. Components 22, 23 and 24 in theFIGURE are provided for this embodiment of the invention.

The above examples are illustrative only. The teachings of thisinvention and the present state of the art in the engine technology andcatalytic reforming and catalytic reactor fields will readily suggest toone skilled in this art suitable designs and procedures in accordancewith this invention for any particular motor type or main fuel to beemployed, as well as other variations within the scope of thisinvention. It should also be recognized from the above that one of themain advantages of the present invention is the large number ofpossibilities which exist for modification of existing systems toencompass the present invention using available components. This is ahighly important, practical advantage of the present invention ascompared to more sophisticated solutions to the extremely important andcontroversial problems discussed above.

The principles, preferred embodiments and modes of operation of thepresent invention have been described in the foregoing specification.The invention which is intended to be protected herein, however, is notto be construed as limited to the particular forms disclosed, sincethese are to be regarded as illustrative rather than restrictive.Variations and changes may be made by those skilled in the art withoutdeparting from the spirit of the present invention.

What is claimed is:
 1. A process for reducing the amount of noxiouscomponents and aldehydes in the exhaust gas of an operating combustionengine which employs a fuel comprising gasoline and methanol comprisingthe steps of:(a) recycling a water vapor-containing exhaust gas streamfrom the combustion engine to a first zone wherein the exhaust gasstream is mixed with a separate feed stream comprising methanol in afixed amount selected from within the range of about 5 to 35 percent byvolume based on the amount of gasoline supplied to the combustion enginewhich is fed from a storage zone through a vaporization zone; (b)catalytically steam reforming said vaporous methanol-containing feedstream in a steam reforming zone in the presence of said exhaust gasstream to form a gaseous mixture comprising hydrogen and carbonmonoxide, whereby at least a portion of the water vapor and energyrequired for said steam reforming is provided by said exhaust gasstream; (c) combining said gaseous mixture of hydrogen and carbonmonoxide with a mixture of air and gasoline; (d) supplying thehydrogen/carbon monoxide/air/gasoline mixture to a combustion zonewithin said combustion engine; (e) combusting said mixture in saidcombustion zone to produce an exhaust gas comprising a reduced amount ofnoxious components and aldehydes.
 2. The process according to claim 1wherein the steam reforming is carried out in the presence of a noblemetal catalyst and at a temperature within the range of 275° to 350° C.3. The process according to claim 1 wherein the steam reforming iscarried out at a temperature within the range of 250° to 400° C.
 4. Theprocess according to claim 1 wherein additional water is delivered tothe steam reforming zone from a water tank.
 5. The process according toclaim 1 wherein the methanol is introduced in an amount of about 10percent by volume based on the amount of gasoline supplied to thecombustion zone.
 6. The process according to claim 1 wherein the ratioof air to primary fuel is about 1:2.
 7. The process according to claim 1wherein the methanol is vaporized in a vaporization zone with heat fromthe exhaust gas stream.
 8. The process according to claim 1 wherein themethanol is introduced in a fixed amount selected from within the rangeof about 10 to 20 percent by volume based on the amount of gasolinesupplied to the combustion zone.
 9. The process according to claim 1wherein the steam reforming is carried out in the presence of a noblemetal catalyst and at a temperature within the range of 200° to 600° C.and wherein the process is continuous.
 10. The process according toclaim 9 wherein prior to performing steps (a) through (e), a fuel streamcomprising at least one lower alcohol is mixed with air and the mixturecombusted within said combustion engine for a period of time sufficientto raise the temperature of the steam reforming zone to within the rangeat which steam reforming is carried out.